Because not all of them will divide evenly.
To change a fraction into a decimal number, you divide the top number
by the bottom number. That is, the top number goes into the division box.
You then put the decimal point after the top number and add as many
zeros on the back end as you like. Upon division, the calculations
will either stop with a remainder of zero or a repeating pattern will
For example: 3/4 = 3 divided by 4 = 4 | 3.00000
On the other hand, the fraction 1/3 = 0.33333333.... = 0.3
where the bar indicates that the digits repeat
23/99 = 0.2323232323 = 0.23
The 7s are interesting creatures. They exhibit the property you are speaking of.
There are no more repeating digits than the denominator.
1/7 = 0.142857 <--- 6 repeating digits
This is because the remainder must be LESS than the number you are dividing by.